Pencil-in-cup deformity

Pencil-in-cup deformity is the description given to one of the appearances on plain radiographs classically associated with psoriatic arthritis.

Radiographic features

The appearance results from periarticular erosions and bone resorption giving the appearance of a pencil in a cup.

Differential diagnosis

Although classically described with psoriatic arthritis, this appearance can also be seen in systemic sclerosisrheumatoid arthritis, or reactive arthritis.

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